Effects of temperature on phosphorus mobilization in sediments in microcosm experiment and in the field

Abstract

The release of phosphorus (P) from sediments may have significant influences on the concentration of water P and the trophic status of lakes. This study investigated the effects of temperature on the mobilization of P in sediments and its release to the overlying water in an incubation experiment and in the field of a shallow Lake Taihu (China). The ZrO-Chelex diffusive gradients in thin films (ZrO-Chelex DGT) and dialysis sampler (Peeper) were used to simultaneously measure labile P/Fe and soluble P/Fe in sediments at vertical resolutions of 2 mm and 4 mm, respectively. The results showed that the mean DGT-labile P and soluble reactive P (SRP) concentrations at 25 °C increased by 279% and 125% in comparison with those at 7 °C in the microcosm experiment, respectively, while in the field the proportions became 460% and 189% respectively. The microbial activity in sediments also increased with the rising temperature. Moreover, positive correlations (p < 0.001) existed between DGT-labile P and labile Fe and between SRP and soluble Fe under different temperature, implying that the mobilization of P and its release to the overlying water was dominantly controlled by Fe redox cycling. This study provided strong evidence that the rising temperature enhanced the microbial reduction of P-hosted Fe (oxyhydr)oxide, while an on-site accumulation and degradation of algal material in the sediment surface may lead to a greater effect on P mobilization.